The invention concerns a thermal switch for temperature control of electrical heating apparatus wherein the stationary end of a contact reed and its opposite contact are mounted, insulated against one another, on a support structure, wherein the contact reed connects in an electrically conductive fashion with a terminal lug and can be so loaded by a bimetallic disk spring that it will lift off the opposite contact.
An electrical thermal switch of this design is previously known from the German published patent application No. 20 57 003. In this prior thermal switch, the feeding of current to the contact reed is accomplished by way of the termial lug made from a rigid stable material, which lug is to resist mechanical loads whereas the contact reed itself is fashioned as a leaf spring whose one end is welded to the terminal lug while its other end supports the contact. A suitable prestress of the spring material produces the necessary contact pressure. The underside of the leaf spring bears on a bimetallic disk spring.
It has been demonstrated that this design has several disadvantages associated therewith:
Making the welding connection between terminal lug and leaf spring is expensive and thus a considerable cost factor. Intolerances in welding, on one hand, but also not completely manageable distortions and curvatures of the leaf spring, on the other hand, affect the reliability of the function, i.e., of the switching operation:
For the production of reliable large-scale products it is important to accomplish a proven switching performance as the bimetallic disk spring responds, that is, the superimposed contact points of leaf spring and bimetallic disk spring must have a defined spacing which is reproducible in mass production with tolerances as narrow as possible. This cannot be completely accomplished with the prior art structures for the above reasons; consequently, considerable quality and functional defects may occur in mass production.